Most Helpful Guy
Most wouldn't. But it certainly possible, especially if the relationship isn't great. As is a women being jealous of her man and his sister. It wouldn't be about the person so much though as jealous of the close relationship they have (wanting it).
Most Helpful Girl
Some men do because the woman could trust her brother more than her boyfriend. The boyfriend wants to be a girl’s #1 go to. The brother is getting in the way of that, in some respects. It’s the same reason guys take issue with a daddy’s girl who listens to her dad over the boyfriend.